ALLISON TRANSMISSION MT643
Serial Number is located on side of transmission on a small plate, you must have it when ordering parts. The external filter is normally located on the right / curb side of the transmission, you will have to look up to see it.

Be careful if you are not using true Allison filters. If your filter has a magnet to pickup floating metal shavings and you should reuse the circular magnet , the non Allison filters will partially block some of the filter circulating holes. They can cause premature failure of the transmissons. When I worked at Williams we carried an example of this to show non Allison filter users. Well worth the couple extra bucks for genuine Allison filters. And I don't even work there any longer...